Airport Safety

Intelligent Airlines Meet Passenger Needs

As airports become stretched to capacity and calls mount for new runways and terminals, a computer scientist in Greece has designed a system that could ensure as many seats as possible are filled on each flight and no one is left stranded at check-in.

Dimitris Kanellopoulos of the Technological Educational Institute of Patras, explains how in recent years, the airline industry has become increasingly dependent on computers for its operational and strategic management. However, the current software tools it uses to match passengers to available seats on flights, is outmoded and inefficient. One of the main problems is that the software simply does not understand the passengers' requirements.

Inspired by earlier work on an employer-employee matching system developed by researchers in Spain, Kanellopoulos is working on an intelligent web portal that will act as a service provider for the airline industry.

The portal will help people living in Europe to find airline seats that match their personal travelling preferences by locking on to the meaning of the keywords with which they describe themselves and their travel needs. For instance, whether they require a shorter than standard check-in time, wheelchair access, frequent-flyer rewards, and to arrive in Paris for a meeting before 3pm of Tuesday next week and whether they have a preference for a no-frills carrier.

This kind of semantic information is then matched against a knowledge database provided by the airlines that represents all the possible options available in terms of time of flights, seating, eating, and check-in arrangements, and other variables.

The knowledge database, works with a special conceptual model known as an "airlines ontology". The model endows the web portal with the necessary understanding of what each passenger requires. According to Kanellopoulos, it extends recent developments in web searching that has allowed travellers to search for seats on different airlines and to hook up their flight to car rental, hotel reservation, vacation packages and other travel products.

The approach is outlined in the International Journal of Computer Applications in Technology. In related work, Kanellopoulos has extended the web

Virgin Galactic Unveils Space Liner Mothership

MOJAVE, California — With all the pageantry of a king's arrival, the WhiteKnightTwo — a huge flying launch pad to support passenger suborbital space travel — is making its public debut here today.

The rollout of the colossal composite plane signals the first phase of a critical test program to establish a private spaceliner business - a venture being bankrolled by British entrepreneur and billionaire, Richard Branson and his Virgin Group.

Looking like a giant catamaran for the sky, the twin-boom, two individual fuselages are topped by a large, 140-foot (42-meter) long stretch of wing. The aircraft will straddle and carry to drop altitude (around 48,000 feet) the SpaceShipTwo — a six passenger, two pilot craft that, once released, rocket's pay-per-view passengers to some 65 miles (104 km) above the Earth.

"This is a big airplane," said Scaled Composites founder, Burt Rutan, and Chief Technology Officer and Chairman Emeritus of the company. "It is not an inappropriate claim to say this is the largest all-composite airplane," he told SPACE.com.

WhiteKnightTwo is the 40th aircraft of varying types to be rolled out by Scaled Composites, Rutan said. "I think that's more than you'll find in any other company by a large margin."

Downsize the uncertainty

While today's show-and-tell festivities are a milestone maker, the true test of the WhiteKnightTwo and its flying attributes are ahead, to be accomplished here at the Mojave Air and Space Port.

Rutan noted that "you can't have schedule pressure before you fly...because that's not a safe thing to do. In terms of what the schedule will be to complete, you really don't know anything until you start flying," he continued, calling it a downsizing of the uncertainty.

"You don't know when you're going to be done until you march through the research flight tests," Rutan emphasized.

Rutan said that the WhiteKnightTwo/SpaceShipTwo system is not a Burt Rutan design.

"We've got some very talented people ... so the credit for thinking and having the courage to try belongs to them," he said, underscoring the expertise of such people as Bob Morgan, Jim Tighe, Matt Stinemetze, and Pete Siebold...part of a team of some 20 engineers that worked on the endeavor. "Of course, they had to sell me on it," he added.

Spacious seating

The WhiteKnightTwo could be ready to do a space launch with only 40 flights — "if everything works," Rutan said, "but more than likely we'll run a few more than that."

Largely driven by the need to snag market share of the public suborbital space tourism business, Rutan said that the WhiteKnightTwo/SpaceShipTwo system is designed to yield a top-notch flight experience.

For one, the SpaceShipTwo offers a roomy — yes, call it spacious — passenger cabin with great windows to afford a ticketed traveler a stunning sight, Rutan said.

Passengers riding in the WhiteKnightTwo launch aircraft will be provided a spectacular view as well - with SpaceShipTwo peeling away and blasting skyward toward space.

"Riding in the launch airplane to watch a launch is going to be a cool thing to do," Rutan pointed out.

Moreover, WhiteKnightTwo will serve as training ground — albeit in the air — for future space travelers. The mega-plane can provide stints of microgravity for next-in-line SpaceShipTwo flyers, Rutan noted, with the aircraft also able to give clientele six to seven Gs to mimic the forces encountered during a suborbital space jaunt.

Too early to say

"For us, this rollout is a really important event," said Will Whitehorn, president of Virgin Galactic. "We're going to be flying in a couple of months ... ground testing starts almost immediately after this event is over," he told SPACE.com.

Whitehorn said that as soon as that ground evaluations are finished and everyone is satisfied "we'll put it into the air ... perhaps in a few weeks or it could be about eight weeks at the maximum."

"When we are all happy ... then it will start flying. That could be very soon ... but there's no exact date," added Whitehorn. "In terms of money spent on the spaceliner system by Branson's Virgin Group to date, he explained: "We're at $100 million that has been spent so far."

As for the readiness of the suborbital SpaceShipTwo, Whitehorn said that the vehicle is now about 70 percent complete.

"Whether or not we fly the spaceship into space next year ... it's too early to say. But the ambition will be to fly it by the end of 2009 or early 2010 into space," Whitehorn explained.

Marketing mode

Spotlighting the scope of what WhiteKnightTwo can provide on its own, Whitehorn switches into marketing mode and offers some suggestions: "I think the market for WhiteKnightTwo will be a lot bigger than we've estimated."

In addition to supporting suborbital space travel, Whitehorn said the WhiteKnightTwo carrier plane can satisfy a range of market needs from satellite launchings to deploying unmanned aerial vehicles, or toting large quantities of water to help squelch raging fires, as well as hauling hefty amounts of cargo from point to point.

Stuart Witt, General Manager of the Mojave Air and Space Port, said there's a significance that might be missed given today's rollout of WhiteKnightTwo.

"It's all about results," Witt told SPACE.com. "That's why people come to Mojave. The WhiteKnightTwo/SpaceShipTwo ... they are one more example of a result that will yield breakthroughs in aerospace. Here at the Mojave Air and Space Port, we're all about results."

Witt said the Air and Space Port is ready to support WhiteKnightTwo and the SpaceShipTwo test program. "I am looking forward for Scaled Composites to get back into the rocket testing business ... and on we go!"

Airbus A400M Airlifter Makes Public Debut

In this photograph, taken at the roll-out of the first Airbus A400M airlifter, the aircraft's advanced-aerofoil propellers are very noticeable. The propellers are made by French company Ratier-Figeac.

Airbus Military has rolled out the first A400M military transport aircraft from the final assembly line for the new airlifter in Seville, Spain.

Designed initially to a requirement from European air forces for a new airlifter, the A400M incorporates materials and technology being used in the newest civil jets. The new aircraft incorporates features such as electronic flight controls, carbon composite structures and an automated handling system.

Launched under a single contract in 2003 with orders for 180 aircraft from seven European launch customers, the A400M is the most ambitious military procurement program ever undertaken in Europe.

Launch customer nations Belgium, France, Luxembourg, Germany, Spain, Turkey and the United Kingdom were later joined by Malaysia and South Africa, which ordered the A400M for their own requirements and brought commitments for the new airlifter to 192 aircraft. Chile, too, has signed a letter of intent to acquire A400Ms.

“This event demonstrates our joint determination to show that EADS can design and manufacture a long-range military transport aircraft which will set new standards in airlift and open further potential in international markets. It also serves to justify the confidence which our customers placed in us when awarding the initial contract,” said Louis Gallois, CEO of EADS, parent of both Airbus Military and Airbus.

The initial 180-aircraft contract, worth some 20 billion euros ($31.16 billion), was signed between Airbus Military and OCCAR, (Organisation Conjointe de Coordination en matiere d’Armement), the contractual body representing all seven European customer nations).

Airbus Military designed the A400M to be versatile enough to offer both tactical and strategic airlift capability. With a payload of up to 37 tonnes over ranges of up to 4,700 nautical miles (5,409 miles), the A400M is designed to carry all loads and vehicles in the European Staff Requirement (ESR) inventory, serve as an aerial delivery platform and act as an in-flight tanker for both fast jets and helicopters.

Typically, the A400M will be capable of carrying a 32-tonne payload over 2,000 miles, and can carry up to 116 paratroopers, according to the UK Ministry of Defence (MOD). It will be able to drop cargo by parachute, by gravity extraction from its loading ramp, or by landing on rough landing strips. The Royal Air Force's A400M fleet will be based at Brize Norton in Oxfordshire, the RAF's main transport-aircraft hub.

The turboprop-powered A400M will be able to travel at speeds comparable with jet transports both at low level and at altitude, according to the MOD. The crew of three, comprising two pilots and a loadmaster, will have available the same advanced flight-deck and cabin technology used in the latest Airbus commercial jet programs, such as the A380.

EADS says the A400M is the first truly new military transport aircraft of its category designed in over 30 years, with twice the capacity and twice the payload of the aircraft types that it will replace in European service.

The A400M is powered by four new-generation TP400-D6 turboprop engines, developed, manufactured and supported by EuroProp International (EPI). EPI is a European joint venture company, the partners of which are Rolls-Royce, Snecma Moteurs, MTU Aero Engines and Industria deTurbopropulsores (ITP).

EPI's TP400-D6 engine is rated at more than 11,000 shaft horsepower. It drives Ratier-Figeac FH386 advanced-airfoil propellers that allow the aircraft to fly up to a cruise speed of Mach 0.72.

Sikorsky's X2: Developing a Faster Helicopter

Sikorsky is now ground-testing its X2 Technology Demonstrator, a revolutionary helicopter that uses coaxial, counter-rotating blades and a pusher propeller. Sikorsky hopes the X2 will fly nearly twice as fast as today's helicopters.

Nearly three years ago, Sikorsky Aircraft announced it would develop technologies — collectively called "X2 Technology" — that would significantly change helicopter flight. Every day thousands of people in the United States travel in helicopters, among them politicians, executives, tourists and patients.

The main advantage of helicopters — categorized as rotary-wing aircraft — is their ability to take off and land vertically. However, compared with fixed-wing aircraft, they are slow. For example, the 12-passenger S-76 helicopter flies at 178 mph, but an 11-seat Beechcraft KingAir 350 turboprop flies at 350 mph, nearly twice as fast.

However, United Technologies Corp. subsidiary Sikorsky Aircraft, the oldest name in helicopter manufacturing, is working to change that by developing a helicopter that will fly almost as fast as a conventional aircraft — without using the mechanically complex and expensive tilt-rotor system pioneered by Bell.

Sikorsky plans a faster helicopter

On June 6, 2005, Sikorsky announced that it would build and test a technology demonstrator that would maneuver like a conventional helicopter and cruise at 250 knots (288 mph), which is at least 60 percent faster than conventional helicopters.

X2 Technology helicopters will affect passenger travel due to substantially reduced flight times. For example, flights between Bridgeport, Conn. and JFK Airport in New York City would be decreased from 40 minutes to 25 minutes. Also, X2 Technology medevac helicopters would be able to transport people in critical condition to hospitals in significantly less time, potentially saving lives.

“We initiated X2 Technology convinced that the most productive and flexible helicopter is a helicopter which is capable of a significant increase in speed,” said Stephen Finger, then-president of Sikorsky Aircraft. “Customers are demanding greater speed but without sacrificing any of the unique capabilities that make helicopters the ideal platform for countless civil and military missions.”

Advanced aerospace technologies

Although the top speed of helicopters has not increased much since the 1960s, improvements in computers, materials, navigation systems, and other aspects of aircraft during the past two generations have been unprecedented.

X2 Technology aircraft will take-off and land vertically, hover, maneuver at low speeds, and transition from hover to forward flight like regular helicopters. However, the new Sikorsky aircraft will have one or more aft-mounted ‘pusher’ propellers, a significant difference in design from helicopters of the past six decades.

Coaxial, counter-rotating blades

Most helicopters have a ‘disc’ of rotating blades on top of the fuselage and shorter blades mounted on the side of the tail that spin in a plane roughly perpendicular to the main disc. The purpose of the aft blades is to provide a counterforce to the torque effect on the fuselage created by the spinning main disc. The X2 Technology Demonstrator has a coaxial rotor system comprised of two hubs with blades attached. The hubs spin in opposite directions, which eliminates the torque effect.

“The X2 Technology Demonstrator is an integrated suite of technologies intended to advance the state-of-the-art, counter-rotating coaxial rotor helicopter. As we continue to work to prove and mature the technologies that will allow the X2 Technology Demonstrator to become a viable product, we are focused on testing its limits and finding out where this technology will take us," Jeffrey Pino, Sikorsky’s president, said recently.

“This could be a ‘game changer’ in the industry,” Pino said of the X2 Technology Demonstrator at Heli-Expo 2008, the main U.S. helicopter convention. "We are diligently pursuing this as a research project. We are testing the limits and pioneering this exciting innovation."

Sikorsky built the X2 Technology Demonstrator in collaboration with subsidiary Schweizer Aircraft, and funded the project entirely by itself. The aircraft continues to make progress toward its first flight, said Peter Grant, Sikorsky's senior manager of Advanced Programs.

“Throughout 2007, the aircraft made excellent additional build and subsystem test progress, re-entering vehicle ground testing in November 2007,” said Grant. "Extensive test instrumentation is also being installed as preparation for its first flight."

No first-flight date yet

Ground testing of the X2 Technology Demonstrator is still underway and Sikorsky hasn't yet scheduled a date for the aircraft's first flight, said company spokesman Paul Jackson.

"Experimental aircraft have minds of their own — sometimes you have to let them proceed at their own pace," said Jackson. "For that reason, we have not targeted any date for the first flight."

Sikorsky Aircraft, has been consulting with helicopter operators to determine how X2 Technology aircraft would benefit their business at a price they can afford. Sikorsky is developing plans to design and build a civilian X2 Technology helicopter that would satisfy operators’ requirements and appeal to the traveling public.

"Certainly civilian travel appears to be a promising market. People will be able to fly back and forth from visits, dates, and meetings twice as fast each way as it now takes by helicopter," said Jackson. "Perhaps a helicopter air taxi market will evolve as many aviation experts have predicted for the small-airplane segment."

B-1B Sniper Pod in Service by Summer

A B-1B Lancer flies on a testing mission carrying a sniper pod on May 16 over Edwards Air Force Base, Calif. The sniper pod is scheduled to be fully operational by summer. Credit: U.S. Air Force photo/Jet Fabara

Air Force officials say the B-1B Lancer sniper pod could be operational as early as this summer after accelerated testing cut the length of the sniper pod program from nine to three months.

Air Force Materiel Command's Global Power Bomber Combined Test Force at Edwards Air Force Base, along with Air Combat Command's 337th Test and Evaluation Squadron from Dyess AFB, Texas, combined the operational and developmental test of a B-1B at Edwards AFB.

"This has been the first time that we have brought (a force developmental evaluation) squadron here," said Lt. Col. Troy Asher, the Global Power Bomber Combined Test Force director and 419th Flight Test Squadron commander. "We have done all flavors of testing here at the same time in the span of about two weeks, which was originally planned for two months. We have knocked out over half of the force developmental evaluation. We have been able to take data from their (operational) testing, and they have been able to take data from our (developmental) testing. It has just been phenomenal."

Typically, the Global Power Bomber Combined Test Force performs the developmental testing on a system as well as the initial stages of operational testing because Air Force Operational Test and Evaluation Center is part of the Combined Test Force. At the end of every program, the B-1B would be sent back to ACC for force developmental evaluation, the final part of operational testing in which tactics and training procedures are developed.

"Developmental test and operational test have different perspectives on what each wants to get out of a test program," said Lt. Col. Christopher Brunner, the 337th TES commander. "We have to be smart and mesh each other's objectives together to ensure not only the system under test is safe and has no major deficiencies, but also it is operationally effective and relevant for the warfighter."

Targeting pod a significant upgrade

"The targeting pod is probably one of the most significant upgrades to the B-1B," said Capt. Brandon Miller, a B-1B flight commander and 419th FLTS targeting pod project pilot. "This is significantly going to decrease the time from a request for a bomb on a target, to actually dropping a weapon, creating the desired lethal effects and then being able to assess and re-attack if necessary."

For more than four years, the B-1B has been a workhorse of the weapons delivery in Iraq and in Afghanistan, Colonel Asher said.

"A lot of times, we are not allowed to drop on targets because we are not exactly sure we wouldn't hit friendlies, or we might hit something we are not supposed to hit," he said.

"With the pod, we can cross check coordinates and visually determine and correlate the target we want to strike," said Maj. Joshua Lane, a 419th FLTS flight test weapons systems officer and assistant director of operations. "The rules of engagement and the instructions in theater are very robust to prevent an aircrew from bombing the wrong target. There's a very deliberate chain that has to be followed. Adding the target identification capability to the chain gives us the level of security we need to accurately strike targets."

Instantaneous feedback

Moreover, through the video downlink on the pod, the new system can provide instantaneous feedback to the joint terminal attack controller, Colonel Brunner said.

"It's very important to remember that this also benefits the warfighter on the ground that the B-1B is supporting," Colonel Asher said. "They are our 'customers' who we are ultimately serving, and anything we can do to get bombs on target quicker, the better."

Combining the developmental and operational tests puts a large strain on the team, the colonel said.

"But it's a testament to how fast we can go if we need to," he said. "If the warfighter has a critical need, we can get it out to them in record time."

Throughout the testing, the team members have been working two and three missions in a given week, said Capt. Brian Neff, a 419th FLTS chief flight test engineer.

Even with setbacks such as system malfunctions, the team has been able to overcome those obstacles and stay on track.

"The main challenge is completing all testing in a safe and timely manner to preserve training time for the operational aircrew before they deploy with this new capability later this summer," Colonel Brunner said. "We were presented with a compressed schedule due to some production delays and aircraft fallout, but in the end it's the great people involved with the program who overcame a lot of adversity and made things happen."

Because the sniper pod is a "desperately needed capability in theater," everyone here has been incredibly focused on getting this done, Colonel Asher said. "We have gotten all of the support we've needed from the Air Force Flight Test Center and all across the Air Force to make this happen."

Airlines Intensify Environmental Efforts

WASHINGTON, D.C. — Pressed on all sides by soaring fuel prices, economic slowdown and poor public perception regarding their environmental performance, airlines in North America are stepping up their environmental sustainability efforts dramatically.

At the first aviation environmental forum ever to be held in the United States, the Eco-Aviation Conference hosted by Air Transport World magazine and Leeham Co. LLC, airlines such as Continental, Air Canada, Northwest, Alaska Airlines and Southwest revealed a wide variety of efforts to improve their fuel efficiency and environmental friendliness.

Alaska Airlines' specially painted Boeing 737 'Salmon-Thirty-Salmon' flies high over the forests of Washington state. In addition to a host of other environmental initiatives, the airline has accelerated the retirement of its fleet of MD-80s and expects to save a considerable amount of fuel, money, and CO2 emissions by becoming an all-737 airline from August 2008. Credit: Alaska Airlines

Various airlines launched environmental initiatives much earlier than is generally realized and have already reaped substantial results, but the public remains largely unaware of the carriers' efforts. One such airline is Continental, whose $12 billion investment in new aircraft since 1997 has reduced its emissions of greenhouse gases (GHGs) by 2 million metric tonnes compared with the amounts produced by the aircraft the new jets replaced, said Leah Raney, managing director of global environmental affairs for Continental.

"We're all doing the same things, we're all doing it right, we're just not marketing ourselves" well as being environmentally responsible, said Jeff Martin, senior director of flight operations for Southwest Airlines.

Both Southwest and Continental also are fitting winglets to hundreds of their Boeing jets. By reducing the ratio of lift to drag on the aircraft's wings as it flies through the air, winglets reduce the amount of fuel used per flight by several percent. Continental already has fitted more than 230 jets with winglets and even though it is planning to retire its older Boeing 737-300s and 737-500s in the next two years, "We're still putting winglets on them, because it saves fuel," said Raney.

Southwest adopting RNP for all flights

Martin used the Eco-Aviation Conference to announce that Southwest would "accept the FAA's call to action to implement performance-based navigation, reducing airspace congestion and carbon emissions."

Southwest has committed to spend $175 million over the next six years to equip its aircraft, develop procedures and charts and train its pilots to fly highly exact Required Navigation Performance (RNP) approaches to and departures from the 64 airports it serves. The airline expects these steps, developed in partnership with the FAA and RNP-route pioneer Naverus, to save it $25 million a year in fuel costs and emit 156,000 tons less of carbon dioxide (CO2) annually.

Known for being able to turn round an arriving aircraft within 20 minutes for its next departure, Southwest has already switched to using gate electric power for its jets while they sit at the gate. The pilots turn off the arriving 737's auxiliary power unit (APU) as it arrives at the gate and ground crew attach an electric power cable to the aircraft. The APU isn’t turned on again until 5 minutes before departure.

EcoPower wash

Southwest also is one of a growing number of customers for Pratt and Whitney's EcoPower wash process that substantially reduces an engine's fuel burn by keeping its compressor blades very clean aerodynamically. The wash forces water through the engine. It is carried out by a specially fitted truck at the gate, which completes the process in less than 90 minutes and recovers and recycles the water used for cleaning as it exits the rear of the engine.

Delta Air Lines, meanwhile, is installing WheelTug electric motors in the nose-wheel hubs of its Boeing 737-800s. Powered by the aircraft's APU, each motor is powerful enough to allow an aircraft as big as a Boeing 767 to back away from a gate, complete turns, and taxi out to the runway at a speed of up to some 21 mph before starting up its engines.

Alaska Airlines, which pioneered the use of RNP flying so that it could reliably land at Juneau, Alaska, which is surrounded by mountains and often has very cloudy weather, represents a typical snapshot of a modern-day airline. It is installing winglets across its fleet, accelerating the retirement of its fuel-hungry MD-80s to become an all-737 airline by August, and using ground power for its aircraft instead of running their APUs while they are at the gate.

Alaska going all-turboprop for regional flights

Expanding the reach and scale of its corporate and on-board-catering recycling efforts, like many other airlines, Alaska Airlines also will be the first U.S. carrier to return entirely to all-turboprop operations for its regional flying.

Horizon Air, Alaska's regional subsidiary, will standardize on an all-Bombardier Q400 fleet by 2009, adding at least 17 more Q400s to the 33 it already has in service. The additional aircraft will replace 21 Bombardier CRJ 700 regional jets now in Horizon Air's fleet, and at the same time the carrier will retire 16 smaller Bombardier Q200 turboprops it has in service, said Scott Ridge, Alaska Airlines' managing director technical operations and support flight operations.

Northwest Airlines has both launched a carbon-offset donation program on its Web site — allowing passengers making bookings to donate to CO2-offsetting programs, if they wish, at costs averaging $12 to $18 per domestic flight depending on trip length — and has created an environmental partnership with The Nature Conservancy, the world's largest conservation organization.

No detail is too small for Northwest to examine in terms of recycling and environmental sustainability. "We've looked at things like 'Do we switch from cans to 2-liter bottles of soft drinks on the plane?'" said Erin Heitkamp, a senior environmental policy engineer with Northwest. The airline has reduced its GHG emissions by 27 percent since 2000, reduced its fuel burn by 575 million gallons, and expects further substantial reductions in the near term with its decision this week to ground in the next few months almost all of the 95 elderly DC-9s remaining in its fleet.

Air Canada's City Pair Cost Index

Air Canada, meanwhile, has developed a unique and powerful method to fly more efficiently. The airline has developed a "City Pair Cost Index" (CPCI) algorithm which divides the total time cost of each minute of a flight made by a particular aircraft by the fuel cost, said Capt. Claude Saint-Martin, Air Canada's manager, fuel efficiency and environmental matters.

Pilots on North American flights then feed the algorithm into the flight management systems of their aircraft. Air Canada intends CPCI eventually to be a four-phase program that would allow dynamic flight-plan adjustment throughout any flight in its network, based on the flight's actual take-off time.

In Part I, which was launched in April 2006, pilots on Air Canada flights within North America that would otherwise arrive early began inputting CPCI indices into their aircraft's flight management systems, allowing the units to calculate if there was a cost and fuel benefit of arriving on time a few minutes later. If there was, the FMS would slow the aircraft down slightly. Air Canada saved 80,000 tonnes of fuel in the first year as a result, emitting some 250,000 fewer tonnes of CO2 into the atmosphere, said Saint-Martin.

Henri Giffard Flies the First Airship

Aviation, term applied to the science and practice of flight in heavier-than-air craft, including airplanes, gliders, helicopters, ornithopters, convertiplanes, and VTOL (vertical takeoff and landing) and STOL (short takeoff and landing) craft (see Airplane; Glider; Helicopter). These are distinguished from lighter-than-air craft, which include balloons (free, usually spherical; and captive, usually elongated), and dirigible airships.

Glider A glider at the Wycombe Air Park receives a wing inspection. A glider, having no engine, relies on aerodynamic forces from upcurrents pushing on its long, narrow wings to fly. Although freeflying, the lightweight gliders must first be towed and launched into the sky by another aircraft.

Helicopter in the City Versatile and maneuverable, helicopters are used to make traffic reports, provide aerial coverage of breaking news stories, perform emergency rescues, and deliver business executives to meetings. Helicopters are particularly useful in cities because of their ability to negotiate crowded areas and land in restricted space.

Operational aviation is grouped broadly into three classes: military aviation, commercial aviation, and general aviation. Military aviation includes all forms of flying by the armed forces-strategic, tactical, and logistical. Commercial aviation embraces primarily the operation of scheduled and charter airlines. General aviation embraces all other forms of flying such as instructional flying, crop dusting by air, flying for sport, private flying, and transportation in business-owned airplanes, usually known as executive aircraft.

Versatile and maneuverable, helicopters are used to make traffic reports, provide aerial coverage of breaking news stories, perform emergency rescues, and deliver business executives to meetings. Helicopters are particularly useful in cities because of their ability to negotiate crowded areas and land in restricted space.

An assistant holds the wing of a glider at the Wycombe Air Park as a tow plane prepares to launch it. A glider, having no engine, relies on aerodynamic forces from upcurrents pushing on its long, narrow wings to fly. Although freeflying, the lightweight gliders must first be towed and launched into the sky by another aircraft. The assistant keeps the wing from dropping until the glider achieves liftoff.